Nutrient Cycles in Marine Ecosystems

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Nutrient Cycles in Marine Ecosystems
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Objectives

• Inputs and outputs to the reservoir of dissolved
  nutrients.
• The biological uses of nutrients.
• Nutrient availability and productivity.

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• Nutrient chemical that an organism needs to live
  and grow (or a substance used in an organisms
  metabolism) which must be taken from the
  environment

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Demonstrate an understanding that there is a
reservoir of nutrients dissolved in the surface
layer of the ocean

• Algae require light for photosynthesis.
• Light intensity decreases as the depth of the
  ocean increases and therefore photosynthesis is
  restricted to a surface layer in which there is
  sufficient light.
• This layer (referred to as the photic zone)
  varies in depth from about 30 m to 150 m,
  although it is considerably less is turbid water.

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Demonstrate an understanding that there is a
reservoir of nutrients dissolved in the surface
layer of the ocean
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Demonstrate an understanding that there is a
reservoir of nutrients dissolved in the surface
layer of the ocean

• The surface layer of the ocean contains many
  different ions, some of which are shown below

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Demonstrate an understanding that there is a
reservoir of nutrients dissolved in the surface
layer of the ocean

• These ions, together with nitrate and phosphate
  ions, form a reservoir of nutrients for the
  growth of algae and other primary producers.
• Nitrate and phosphate ions occur at low
  concentrations in seawater
• the mean concentration of nitrate is 0.5 parts
  per million (ppm)
• the mean concentration of phosphate in seawater
  is 0.07 ppm.

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The Sea-Surface Microlayer

• incredibly thin (few hundred µm)
• important for the chemistry of the ocean
• covers 71 of surface of the planet therefore
  it is the largest single ecosystem
• not well understood (difficult to sample such a
  tiny vertical section of the water column)
• critical link between ocean and atmosphere

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• Receives and transmits
• Energy/gases/solids
• Collects matter transported by winds from above
  and by water below

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The Sea-Surface Microlayer

• Especially dense concentration of minerals,
  organic chemicals, protozoans and
  micro-organisms.
• Upper 70 mm has dense concentrations of slightly
  larger organisms, including fish eggs, fish
  larvae, and crustaceans. Larger, floating
  jellyfish and seaweeds are found in the upper 30
  cm. There are many transient creatures that move
  up and down in tune to the sunlight.

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• The plants and animals that live in the water
  excrete many organic compounds, such as amino
  acids, proteins, and fatty acids that serve as
  nutrients for bacterial growth. These rise to the
  surface where they are concentrated the thin
  organic skin of the water. This happens in fresh
  water as well as salt water.
• When aquatic organisms die, the oils in their
  bodies may float to the surface before they
  completely decompose.
• The thin layer of oily material on the surface
  of the sea is an important part of the water
  cycle as it helps control the rate of
  evaporation. It is also a highly nutritious food
  source for many species of microscopic plants and
  animals (ie plankton).

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The Sea-Surface Microlayer

• Wind pushes the oil into long ribbons of calm
  water known as "wind slicks" or "wind rows."
• You can see these on most days when looking at
  the sea from an overlook or from a boat.
• Samples show the plankton and nutrients are
  thousands of times more concentrated in the
  windrows than in water only a few cm deeper or in
  adjacent areas.
• Unfortunately, the oily surface of the sea is
  also the first to receive pollutants from the
  atmosphere. Scientists believe more than 30 per
  cent of all ocean pollution comes from tiny
  particles of dust and smoke in the air - often
  called fallout.
• This settles on the most sensitive and vulnerable
  part of the ocean - its skin.
• The pollutants contain pesticides, heavy metals,
  and industrial and motor vehicle toxins such as
  sulphuric acid, chlorine, and dioxin.

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Wind Slicks

• Windslick research link

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The Sea-Surface Microlayer

• A polluted surface microlayer has the potential
  to poison much of the complex marine food web,
  including fish, crustaceans, whales, and
  seabirds.
• Destruction of the microlayer may alter the
  exchange of materials between the atmosphere and
  the ocean, thereby affecting global climate.
• Oil pollution also floats on the surface of the
  sea and quickly contaminates this fragile
  environment with chemical toxins.
• Oil, even a very thin layer, spreading over the
  surface of the water at the same time fish are
  releasing their floating eggs can devastate their
  reproductive success

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The Sea-Surface Microlayer

• Heavy metals, and other toxins, are hundreds of
  times more concentrated in the surface windrows
  of the sea than in deeper water. Pesticides are
  found concentrated millions of times greater than
  in the rest of the water.
• As the ozone layer in the upper atmosphere breaks
  down from air pollution, ultraviolet radiation
  increases. This has been shown to have a severe
  impact on the phytoplankton and the eggs of sea
  creatures when they concentrate at the surface.

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Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling from land and dissolving atmospheric
gases.

• Upwelling is the movement of water from deep in
  the ocean to the surface layer, where the
  nutrients become available to primary producers.
• brought about by several processes including the
  deflection of deep water currents upwards and the
  movement of water away from a coast by the action
  of wind.

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Upwelling refers to deep water that is brought to
the surface.
Areas of upwelling are created by surface winds
that pull water away from an area. This deficit
of water on the surface invites water to come up
from deeper regions.
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Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling, runoff from the land, and dissolving
of atmospheric gases

• Upwelling is the movement of water from deep in
  the ocean to the surface layer, where the
  nutrients become available to primary producers
• Upwelling brought about by several processes
• Deflection of deep water currents upwards
• Movement of water away from the coast (due to
  wind)
• Upwelling Animation

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Mechanisms that create ocean upwelling

• Wind
• Coriolis Effect
• Ekman Transport

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Due to friction between the layers of water in
the ocean and the Coriolis Effect, the net result
of wind blowing across the surface of the water
is transportation of a layer of water 90 degrees
to the direction of the wind. This is known as
Ekman Transport.
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To understand upwelling, you must be familiar
with how the Coriolis Force affects ocean surface
currents. The Coriolis Effect acts on moving
water, because it is not attached to the rotating
Earth. As water flows over the rotating earth,
it appears to deflect to the right in the
Northern Hemisphere and the left in the Southern.
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• Coriolis Effect link
• Coriolis Video

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Seasonal upwelling
Wind
Wind
Onshore winds pile water up on shore, thus
surface water will be forced downward. This is
downwelling.
Offshore winds take water away from shore, thus
water from depth will upwell to the surface.
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Even though upwelling areas account for only 1
of the ocean surface, they support 50 of the
worlds fisheries.
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Productivity (phytoplankton growth) of an area
is determined by the rate and the duration of
upwelling.

• Rate of upwelling determines phytoplankton cell
  size.

• Duration of upwelling determines the total amount
  of phytoplankton.

small vs. large
few vs. many
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-Moderate rates of upwelling for long duration (8
months or longer) provide the ultimate
combination for a large fishery. -With too low
or too high a rate, phytoplankton are small, so
there is a trophic level between the algae and
the fish.therefore the fish receive less energy.
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Classification of upwelling systems in terms of
rate and duration
After Thurman, H.V. (1994)
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Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling from land and dissolving atmospheric
gases.

• Run-off from the land is part of the hydrological
  cycle and the water may leach nutrients,
  including nitrates and phosphates, from the soil.
  
• Carbon dioxide in the atmosphere dissolves in
  seawater forming hydrogen carbonate ions (HCO3),
  making carbon dioxide available for fixation in
  the process of photosynthesis, by primary
  producers.

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Show that each of the nutrient cycles listed
below can be summarized as shown in Fig 4.1 and
state the biological use of each nutrient

• nitrogen which is used to make proteins
• carbon which is used to make all organic
  materials
• magnesium which is used to make chlorophyll
• calcium which is used to make bones, corals, and
  shells
• phosphorous which is used to make DNA and bone

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• Figure 4.1 summarizes the ways in nutrients are
  cycled in marine ecosystems. Nutrients may be
  derived from both land and the atmosphere,
  forming a reservoir in the surface layer of the
  sea.
• From here, nutrients are taken up by living
  organisms and incorporated into food chains.
  Nutrients may be removed by harvesting, sinking
  to the sea bed, or incorporation into coral
  reefs. Nutrients from the sea bed may be returned
  to the surface layer of the sea by the process of
  upwelling.

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Ecology
Biological Processes Geological Processes
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The Carbon Cycle

• Key role in Earths thermostat
• Absorbed by ocean, utilized by plants in
  photosynthesis, humans in digestion
• Sinks (storage) in lithosphere (largest reservoir
  limestone and other sedimentary rock),
  hydrosphere (ocean), atmosphere (CO2) and in the
  biosphere (dead animals, wood, plants)
• Released by fires, decomposition, volcanoes, and
  human respiration

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The Oxygen Cycle

• Essential for animals
• Taken in during respiration
• Released by plants in photosynthesis
• Disrupted by the same factors that disrupt the
  carbon cycle
• Clear cutting of trees
• Increased burning of fossil fuels
• Pollution to phytoplankton containing water

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The Nitrogen Cycle

• 78 of troposphere is N2, 0 utilized in
  respiration
• Present in proteins, moves through food chain
• Most complex cycle
• Disrupted by
• Burning fuel (releases nitric oxides)
• Increased use of fertilizer
• Removal from topsoil
• Addition to aquatic ecosystems

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Nitrogen Cycle

• N2 gas is modified by nitrogen fixing bacteria
  into ammonia (NH3) (nitrogen fixation)
• Bacteria turn nitrogenous waste and detritus into
  ammonia (ammonification)
• NH3 is converted into nitrite (N02) which is used
  to produce nitrate (N03) (nitrification)
• Other bacteria convert nitrite into gas which
  enters the air (denitrification)

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The Phosphorous Cycle

• Very slow process
• Found only in sedimentary rocks and water (not in
  atmosphere)
• Released as rocks erode
• Travels through food chain
• Released by decomposition

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The Sulfur Cycle

• Most stored underground
• Released by volcanoes and swamps
• Plants assimilate the sulfur
• Bacteria break it down
• 99 of all that reaches atmosphere is by humans
  (industries, burning fuel, refining petroleum)

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Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling from land and dissolving atmospheric
gases.

• Atmospheric nitrogen gas is fixed by blue-green
  algae in Intertidal zones, resulting in the
  formation of nitrogen-containing organic
  compounds. In this way, nitrogen can enter marine
  ecosystems.

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Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling from land and dissolving atmospheric
gases

• Some nutrients, including nitrates and phosphates
  are also recycled in the surface layer of the
  ocean as a result of excretion from zooplankton.

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Demonstrate an understanding that the reservoir
of dissolved nutrients is depleted by uptake
intoorganisms in food chains.

• One of the ways in which nutrients are removed
  from the surface waters of an ocean is by their
  uptake by primary producers, (phytoplankton) and
  their use for the synthesis of organic
  substances.
• EX, nitrate ions are used in the synthesis of
  amino acids and proteins. If the phytoplankton is
  eaten by zooplankton, the proteins will pass to
  the next trophic level.
• Zooplankton may subsequently be eaten by small
  fish and, in this way, nutrients are passed along
  a food chain.

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Explain how productivity may be limited by the
availability of dissolved nutrients.

• Inorganic nutrients, such as nitrate ions and
  phosphate ions are essential for the growth of
  primary producers. Since consumers depend on
  these primary producers for food, either directly
  on indirectly in food chains, the productivity of
  the primary producers will influence the
  productivity of higher trophic levels. In water
  where the nutrient levels are high, for example
  as a result of upwelling, the productivity is
  correspondingly high. One of the most productive
  ecosystems is the Benguela upwelling system, off
  the west coast of southern Africa.

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Phytoplankton photosynthesize using specialized
color pigments called chlorophyll. Thus, Ocean
Color maps are another way to identify areas of
upwelling. Where on this ocean color map are
high phytoplankton concentrations?
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Demonstrate an understanding that the nutrients
taken up by organisms in food chains may sink to
the sea floor in faeces or after death, may be
incorporated into coral reefs, or may be removed
by harvesting

• Detritus (decaying organic materials), feces and
  dead organisms may gradually sink to the sea
  floor. This represents a loss of nutrients from
  the surface water. In deep water, these nutrients
  will tend to remain on the ocean floor, unless
  returned to surface waters by upwelling.
• The growth of corals involves the deposition of
  calcium carbonate this represents another way in
  which nutrients may be removed from water.
• Harvesting fish and other marine organisms, also
  results in the loss of nutrients from marine
  ecosystems.

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Stormwater Runoff

• the most common pollutant of streams, rivers, and
  oceans.

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Demonstrate an understanding that the reservoir
of dissolved nutrients is depleted by uptake into
organisms in food chains
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Primary production is the total amount of carbon
(C) in grams converted into organic material per
square meter of sea surface per year (gm C/m2/yr).
General Marine Productivity

• Factors that limit plant growth and reduce
  primary production include solar radiation and
  nutrients as major factors and upwelling,
  turbulence, grazing intensity and turbidity as
  secondary factors.
• Only 0.1 to 0.2 of the solar radiation is
  employed for photosynthesis and its energy stored
  in organic compounds.

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• Macronutrients and micronutrients are chemicals
  needed for survival, growth and reproduction in
  large and small quantities, respectively.
• Upwelling and turbulence return nutrients to the
  surface.
• Overgrazing of autotrophs depletes the population
  and leads to a decline in productivity.
• Turbidity reduces the depth of light penetration
  and restricts productivity even if nutrients are
  abundant.

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Productivity varies greatly in different parts of
the ocean in response to the availability of
nutrients and sunlight.

• In the tropics and subtropics sunlight is
  abundant, but it generates a strong thermocline
  that restricts upwelling of nutrients and results
  in lower productivity.
• High productivity locally occurs in areas of
  coastal upwelling, in the tropical waters between
  the gyres, and in coral reefs.

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• In temperate regions productivity is distinctly
  seasonal.
• Polar waters are nutrient-rich all year but
  productivity is only high in the summer when
  light is abundant.

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Variations in Primary Productivity
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Mixing plays an important role in the limitation
of primary production by nutrients.

• Mixing plays an important role in the limitation
  of primary production by nutrients.
• Inorganic nutrients, such as nitrate, phosphate,
  and silicate acid are necessary for phytoplankton
  to synthesize their cells and cellular machinery.
  
• Because of gravitational sinking of particulate
  material (such as plankton, dead or fecal
  material), nutrients are constantly lost from the
  photic zone, and are only replenished by mixing
  or upwelling of deeper water.
• Summer increased solar heating, reduced winds
  leads to vertical stratification (thermocline)
  which makes it more difficult for upwellings

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Mixing plays an important role in the limitation
of primary production by nutrients.

• Between mixing events, primary production (and
  the resulting processes that leads to sinking
  particulate material) constantly acts to consume
  nutrients in the mixed layer
• In many regions, this leads to nutrient
  exhaustion and decreased mixed layer production
  in the summer
• Even in the presence of abundant light not
  always a limiting factor!
• As long as the photic zone is deep enough,
  primary production may continue below the mixed
  layer where light-limited growth rates mean that
  nutrients are often more abundant

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Primary productivity varies from 25 to 1250 gm
C/m2/yr in the marine environment and is highest
in estuaries and lowest in the open ocean.

• In the open ocean primary productivity
  distribution resembles a bulls eye pattern
  with lowest productivity in the center and
  highest at the edge of the basin.
• Water in the center of the ocean is a clear blue
  because it is an area of downwelling, above a
  strong thermocline and is almost devoid of
  biological activity.

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• Continental shelves display moderate productivity
  between 50 and 200 gm C/m2/yr because nutrients
  wash in from the land, and tide- and wave-
  generated turbulence recycle nutrients from the
  bottom water.
• Polar areas have high productivity because there
  is no pycnocline to inhibit mixing.
• Equatorial waters have high productivity because
  of upwelling.
• Centers of circulation gyres, which occupy most
  of the open ocean, are biological deserts.

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The Sargasso Sea and Vertical Profiles
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Remember.

• Although rate of productivity is very low for the
  open ocean compared to areas of upwelling, the
  open ocean has the greatest biomass productivity
  because of its enormous size.

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DETRIVORES AND DETRITUS

• Some heterotrophs (e.g., earthworms, flies,
  beetles, crabs, sea cucumbers, ants, vultures,
  hyenas, etc.) depend on detritus (dead organic
  material/biomass), rather than live organic
  material.
• Note animals can be both a herbivore and a
  detrivore, or a carnivore or omnivore and a
  detrivore, i.e., they eat both living and dead
  organisms.

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DECOMPOSERS

• Decomposers play a very important role in
  mineralisation by breaking down organic
  substances into inorganic compounds that are
  again available for reuse by producers.